Reynolds said the key to the game's success, along with that of "FarmVille" has been a simple structure with increasing depth and subtlety baked in. He said he believes that what people want out of such so-called "Social games" is to see what their friends are up to, whether it's through a Facebook feed or within the games themselves. While some game designers aim to keep players engaged for long stretches of time, Reynolds said games like "FrontierVille" are meant to be played in 15-20 minute increments.

They are games that can be played while people are at work or at school, "when you're supposed to be doing something else," he said.

The "FrontierVille" team has made it a practice to keep inserting things into the game and gauging their success while ripping things out that don't. He pointed to the addition of animals, "Varmints" in the wild, that proved to be successful as well as the ability to build family members. Reynolds said that making one's spouse is the most fun that some people have in the game.

As to how to get people into the game, he said, "Learning is hard. Going to school is no fun." Zynga, he said, tries to make its tutorials fun and engaging and to make learning how to play the game as seamless as possible.

Good game designers, he said, pay attention to behaviors that emerge organically in the game, even if they're inadvertent. He pointed to an incident where a humour cartoon image of a female character next to a sheep was one of the most shared "FrontierVille"-related item shared on Facebook feeds. Zynga embraced the humor of the situation and enjoyed watching the meme spread.